JPH05341734A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To realize a liquid crystal display device for multi-gradation of low cost by suppressing increasing of numbers of constitution of a data bus driver when multi-gradation display is performed constituting with plural cells which can control independently display elements. CONSTITUTION:In a liquid crystal display device, display elements 500, is constituted of 7 plural cells 400A, 400B, each cell in the display elements are connected to the same data bus line 20,... via switching means 300A, 300B, connected to scanning bus lines 10A, 10B,... in which gates are different, and this device is constituted so that a scanning signal is supplied to the scanning bus lines 10A, 10B... with different timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device for multi-gradation display, and more particularly to a liquid crystal display device in which one pixel is composed of a plurality of independently controllable cells.

[0002]

2. Description of the Related Art Liquid crystal display devices in which the display state of each display pixel can be independently controlled are widely used. Liquid crystal display devices are thin and have low power consumption. It is widely used as a display terminal. The present invention can be applied to a liquid crystal display device regardless of a simple matrix system and an active matrix system, but here, the following description will be given by taking an active matrix system using a TFT as an example.

In OA equipment such as personal computers in which liquid crystal display devices are mainly used, there is a demand for higher performance in graphic display, and liquid crystal display devices are also required to have a multi-gradation display function. The most common method of displaying multiple gradations on a liquid crystal display device is to change the voltage applied to the liquid crystal cell according to the gradation level.

FIG. 6 is a diagram showing a basic configuration of a liquid crystal display device in which an applied voltage is changed according to a gradation level. In FIG. 6, reference numeral 600 denotes a liquid crystal panel, and the liquid crystal electrode 6 is provided at the intersection of the scanning bus lines 61 ₀ , 61 ₁ , ... And the data bus lines 62 ₀ , 62 ₁ , ... Arranged in two vertical directions.
4 _00, etc. are arranged in a matrix. Display electrode 6
4 _00, the gate is connected to the data bus lines 62 ₀ through the thin film transistor (TFT) 63 ₀₀ connected to the scan bus line 61 _0. A scan signal is sequentially applied to each scan bus line with a frame display cycle as one cycle. The TFT connected to the scan bus line to which the scan signal is applied is turned on, and the voltage of each data bus line at that time is applied to each display electrode. When the application of the scanning signal to the scanning bus line is completed, the TFT is turned off, and the voltage applied to the display electrode is held until the next scanning signal is applied. As the voltage applied to the liquid crystal, a voltage of positive / negative reverse polarity is applied for each frame. Liquid crystal is filled between the display electrode and the common electrode facing the display electrode. Note that the display electrode, the liquid crystal, and the like are collectively referred to as a display pixel here.

The above is a description of a normal active matrix type liquid crystal display device, and there are other slightly different types such as a facing type, but the explanation is omitted here. Applying a scan signal and a data voltage to the scan bus line and the data bus line of the liquid crystal panel 600 is called a scan bus driver and a data bus driver. Figure 6
In, the shift register 661 and the driver 662 form a scan bus driver, and the shift register 671, the latch 672, the selector 673, and the driver 674 form a data bus driver. A control unit 68 generates a timing signal. Reference numeral 69 denotes a grayscale voltage generation unit that generates a data voltage of each grayscale applied to the data bus line.

A shift register 661 forming a scan bus driver generates a pulse for starting a frame with a vertical synchronizing signal (VSYNC), and a horizontal synchronizing signal (HSYNC).
The line position to be turned on is sequentially moved according to C). The driver 662 applies the output from the shift register 661 to the scan bus line. The shift register forming the data bus driver receives the digital data representing the gradation inputted from the outside, and sequentially shifts by the number of data bus lines according to the clock signal from the control unit 68. The latch 672 latches the output of the shift register 672 according to HSYNC when the horizontal data shift is completed. The selector 673 selects the corresponding grayscale voltage from the grayscale voltage generation unit 69 based on the grayscale data for each data line from the latch 672. And this driver 6
74 applies to the data bus line.

The above is the description of the method of performing multi-gradation display by changing the voltage applied to the liquid crystal cell. However, this method can realize only about 10 gradation voltages of the data bus driver, so that There is a problem that it is not possible to finely adjust the gradation. As another method of multi-gradation display, one display pixel is composed of a plurality of independently controllable cells, and the number of cells in the ON state and the number of cells in the OFF state are increased. There is a method of displaying gradation.

FIG. 7 is a diagram showing one display pixel of a conventional example in which the above-mentioned display pixel is composed of a plurality of cells which can be independently controlled. In the figure, 71 is a scanning bus line, and 72A and 72B are data bus lines. 74A
And 74B are two cells that form a display pixel, and TFTs 73A and 7 whose gates are connected to the scan bus line 71
Data bus lines 72A and 72B are respectively connected via 3B.

Although the display pixel is composed of two cells in FIG. 7, a finer gradation can be expressed by increasing the number of cells. However, since the display pixel is divided into a plurality of cells, there is a problem that the number of cells is increased as a whole, resulting in an extremely high cost. Therefore, multi-tone display is performed by combining the above two methods. This is, for example, a method of applying voltage levels corresponding to gradations to the data bus lines 72A and 72B of FIG. 7, and if the same kind of data bus driver capable of displaying four gradations is used, the respective data bus drivers 72A and 72B will be described. In the case of driving, 7 gradation display is possible by combining the display states of the cells as shown in Table 1.

[0010]

[Table 1]

[0011]

As shown in FIG. 7, in the multi-gradation liquid crystal display device in which a method for applying an applied voltage in multiple stages and a method for dividing a display pixel into a plurality of cells are combined, the number of cells is increased. Only increasing the data bus line.
In addition, these cells need to be independently controllable, which increases the number of circuits inside the data driver.

As is clear from the description based on FIG. 6, when the voltage applied to the data bus line is changed according to the gray scale, the data bus driver is more complicated than the scan bus driver, and is larger by that amount. It requires a mounting area and is expensive. Therefore, the increase of the data bus lines as shown in FIG. 7 causes problems of cost increase and size increase.

In a personal computer, it is usually 64
Since it has a display screen of 0 × 400 dots, there are 400 scanning bus lines and 640 data bus lines. Moreover, in the case of color display, the number of data bus lines is tripled to 1920, so that it is very difficult to increase the number of data bus lines according to the number of divisions into cells as shown in FIG. There's a problem.

An object of the present invention is to solve the above problems and to increase the number of data bus lines and data bus driver in a liquid crystal display device in which a display pixel is composed of a plurality of cells to enable multi-gradation display. The purpose is to suppress the increase in the number of circuits inside.

[0015]

FIG. 1 is a basic configuration diagram showing the principle of the present invention, showing a part of a display panel of a liquid crystal display device of the present invention in which a display pixel is composed of two cells. There is. In FIG. 1, 1 _0A , 1 _0B , 1 _1A and 1 _1B are scan bus lines, and 2 ₀ and 2 ₁ are data bus lines. Reference numerals 5 ₀₀ , 5 ₀₁ , 5 ₁₀ and 5 ₁₁ denote display pixels. Each display pixel is composed of a plurality of cells. For example a unit display cell 5 ₀₀ is composed of A cells 4 _00A and B cell 4 _00B. Each cell in the display pixel is connected to the same data bus line through the switching means whose gates are connected to different scanning bus lines. Ie, A cell 4 _00A is connected to the data bus line 2 ₀ through the switching means 3 _00A having a gate connected to the scan bus line 1 _0A, B cell 4 _00B has a gate connected to the scanning bus line 1 _0B through the switching means 3 _00B, are connected to the same data bus line 2 _0. Scan signals are supplied to the scan bus lines _10A and _10B at different timings.

[0016]

In order to perform gradation expression, it is necessary that each cell in the display pixel can be controlled independently. FIG. 2 shows an example of signal waveforms for driving the liquid crystal display device of the present invention having the configuration of FIG. 1, (a) is an interlace system, and (b) is a continuous cell in a display pixel. It is a method of driving.

In FIG. 2 (a), the VSYNC signal is a vertical synchronizing signal which represents a period for scanning the liquid crystal panel from top to bottom, and here, two pulses are generated while the screen of one frame is displayed. It Two periods defined by the VSYNC signal are a frame and b frame. In the a frame, scan signals are sequentially applied from the top to the bottom of the scan bus lines on which A is added to the number of the scan bus lines, and the switching means connected thereto are sequentially turned on. The voltage of the data bus line is sequentially written in the A cell. During the a-frame, since the scan signal is not applied to the scan bus line on the side represented by B, the B cell is not written and the state is maintained.

On the other hand, in the b frame, the B cell is written, and the A cell holds the state written in the a frame. By applying the drive signal as described above, writing can be independently performed in each cell. FIG. 2B shows an example in which each cell in a display pixel is continuously driven. When a scan signal is applied to the scan bus line on the A side, the next scan bus on the B side is next. A scanning signal is applied to the line.

The above is an example in which the display pixel is composed of two cells, but the same is true when the display pixel is composed of three or more cells. If the data bus driver is capable of applying multi-step voltages corresponding to gradation display, finer gradation expression is possible. For example, if two cells have the same area and the data bus driver can output a voltage in four steps, gradation expression in seven steps as shown in Table 1 is possible.

[0020]

FIG. 3 is a diagram showing a first embodiment of the present invention. In FIG. 3, reference numeral 300 denotes a liquid crystal panel, which has the same configuration as that in FIG. That is, one display pixel is composed of two A cells and B cells of the same area, the scanning bus line is also divided into a group of A and B, and the scanning signal is applied to the corresponding scanning bus line on the A side of the A cell. When the scanning signal is applied to the B side scanning bus line, the B cell is connected to the same data bus line. Switching means is TFT
Is.

Reference numerals 36A and 36B denote first and second scanning bus drivers provided on both sides of the liquid crystal panel 300.
Scan signals are applied to the scan bus lines of the groups B and B, respectively. Reference numeral 37 is a data bus driver, and 38 is a signal generator for generating a control signal. The first power supply 39A and the second power supply 39B are portions that generate a voltage level applied to the data bus line by the data bus driver 37, and are the first power supply 3
9A is the final display level from 0 to 0.3 from 0.1
The second power supply 39B generates a voltage for displaying 0 to 1.2 in four steps every 0.4. Reference numeral 391 denotes a switch for switching the power supply input to the data bus driver 37, which is controlled by a frame signal.

FIG. 4 is a diagram showing a part of the control signal in the first embodiment. Each frame is divided into an a frame and a b frame. The VSYNCA signal input to the first scanning bus driver 36A is a signal for generating a pulse at the start of the a frame, and the first scanning bus driver 36A
In response to this, sequentially applies a scanning signal to the scanning bus lines of the set A in the frame a. The same applies to the VSYNCB signal. The frame signal is in the “low” state during the a frame, and is in the “high” state during the b frame. The switch 391 receives this frame signal, connects the first power supply 39A to the data bus line 37 during the a frame, and b
The second power supply 39B is connected to the data bus line 37 during the frame.

Table 2 shows combinations of gradations that can be expressed in the first embodiment.

[0024]

[Table 2]

Since the first power source 39A is connected to the a frame, 0, 0.1, 0.2, and
There are 4 stages of 0.3, and similarly, B cells can represent 4 stages of 0, 0.4, 0.8 and 1.2. Therefore, one display pixel can be combined as shown in Table 2, and a total of 16 gradations can be expressed. In the first embodiment, the cells have the same size, but it is possible to use other arbitrary ratios. The second embodiment has a cell structure in which the area ratio of the A cell and the B cell is 1: 2 as shown in FIG. Other parts are the same as those in FIG. 3, but it is assumed that only the second power supply 39B generates the display voltage in four steps from 0 to 0.6 in 0.2 steps.

Table 3 shows combinations of gradations that can be expressed in the second embodiment.

[0027]

[Table 3]

Also in this case, continuous 16 gradations can be expressed. The second embodiment has an advantage that the voltage range of the second power supply can be made smaller than that of the first embodiment. Next, let us consider the conditions that enable maximum gradation expression in continuous gradation expression when one unit pixel is composed of two cells. Now, the cell area ratio is a: b (a <b). When an n-gradation data driver is used, the data driver input voltage when driving a cell of size a is V
0, V0 + VA, ... V0 + (n-1) .VA, the input voltage of the data driver when driving the cell of size b is V0, V0 + VB, ... V0 + (n-1) .V.
By setting B (however, VB = n · a / b · VA), the gradation of n ² can be realized as shown in Table 4.

[0029]

[Table 4]

Although the above embodiment has been described with a two-division structure, it may be divided into three or more. Further, the power supply to be supplied to the data driver is switched on a frame-by-frame basis, but it may be switched every few lines. Furthermore, the TFT-LCD was used as the liquid crystal panel, but the STN-
It may be used for a liquid crystal display having a simple matrix structure such as LCD. Further, the present invention can be applied to other active matrix type display devices.

[0031]

As described above, according to the present invention, the number of complicated and expensive data bus drivers is reduced when a pixel is divided into independently controllable cells to perform multi-gradation display. Therefore, an active matrix type display device capable of expressing gradation can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing the principle of the present invention, showing a part of a display section of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing an example of signal waveforms in the configuration of FIG.

FIG. 3 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 4 is a diagram showing control signals in the first embodiment.

FIG. 5 is a diagram showing a cell configuration in a second embodiment.

FIG. 6 is a diagram showing a basic configuration of an active matrix type liquid crystal display device which performs multi-gradation display by changing a voltage applied to a data bus line according to a gradation.

FIG. 7 is a diagram showing a conventional example in which a display pixel is composed of a plurality of cells.

[Explanation of Codes] 1 _0A , 1 _0B , 1 _1A , 1 _1B ... Scanning bus lines 2 ₀ , 2 ₁ ... Data bus lines 3 _00A , 3 _00B , 3 _01A , 3 _01B ... Switching means 4 _00A , 4 _01A ... A Cell 4 _00B , 4 _01B ... B cell 5 ₀₀ , 5 ₀₁ , 5 ₁₀ , 5 ₁₁ ... Display pixel

Claims (5)

[Claims] 1. A liquid crystal display device, the display pixel (5 _00, ...), a plurality of cells (4 _00A,
4 _00B, consists of ...), each cell of the display pixels, the scan bus lines gate are different (1 _0A, 1 _0B, connected switching means (3 _00A to ...), 3 _00B, ...) through the _Are connected to the same data bus line (2 ₀ , ...) And the scanning signal is supplied to the scanning bus line (1 _0A , 1 _0B , ...) At different timings. .. 2. The liquid crystal display device according to claim 1, wherein the cells in the display pixel have different areas. 3. The applied voltage supplied to the data bus line when each display cell in the display pixel is connected to the data bus line is different for each display cell. Item 2. The liquid crystal display device according to item 1. 4. The applied voltage supplied to the data bus line when each display cell in the display pixel is connected to the data bus line is different for each display cell. Item 3. The liquid crystal display device according to item 2. 5. The liquid crystal display device according to claim 4, wherein the display pixel is composed of two cells having an area ratio of a: b, and each of the cells has a maximum unit of VA and VB as a minimum unit. A voltage obtained by adding a voltage up to -1 step to the basic voltage V0 can be applied, and when a is smaller than b, VB = (n
The liquid crystal display device according to claim 4, wherein the liquid crystal display device has a relationship of VA · a) / b.